Not sure if it is relevant, but I understand that up trains will use the direct route from Greenford to Old Oak Common along the little used single line, and down services will run via the Greenford branch.
Interesting. For the Chiltern diversions, they were basically using the Park Royal - Greenford stretch as an extended passing loop, and running two trains per hour it was pretty busy. When I travelled down from Padd - West Ruislip, we had to wait two or three minutes at Greenford's down home for the up train to clear the single line from Northolt. When the up WS&
MR▸ train turned up, the opposing down Chiltern train had to wait there for
two trains to go through -
see the little film I made.
Of course the other deep irony about that day was that there they were running a Paddington - Birmingham Snow Hill service again after all these years!